The present disclosure relates to a semiconductor device. For example, the present disclosure relates to a semiconductor device including a power amplifier that generates a transmission signal for driving an antenna based on two-phase pulses.
In recent years, an IoT (Internet of Things) concept in which products that were not connected to a network in the past are connected to a network all the time and controlled through the network has been proposed. In this IoT concept, it has been considered that, for example, a smart meter, a gas meter, or an infrastructure management product such as a product for building management is enabled to be connected to a network. In this IoT concept, radio signals whose carrier-wave frequency is in a sub-giga Hz band, i.e., is no higher than 1 GHz are used in some cases. Compared to radio signals in a 2.4 GHz band, radio signals in the sub-giga Hz band are excellent in terms of a communication range, a diffracting property of radio signals, or power consumption, and hence are suitable for use as communication signals for products that are assumed to be used in the IoT concept.
Note that in radio communication, a transmission signal for driving an antenna is generated by a power amplifier. This power amplifier is required to have high power efficiency in order to reduce the power consumption. However, the power efficiency has a tradeoff relation with a harmonic distortion characteristic. Therefore, in order to meet communication standards, the harmonic distortion characteristic is satisfied at the sacrifice of the power efficiency. To alleviate this tradeoff relation, Japanese Unexamined Patent Application Publication No. 2015-115946 discloses an example of a technique for reducing a harmonic distortion.
A harmonic cancellation circuit for power amplifier disclosed in Japanese Unexamined Patent Application Publication No. 2015-115946 is a circuit including: an input port for applying a sine wave input signal; first buffer means for converting the sine wave input signal into a rectangular-wave signal; and an output port for outputting the rectangular-wave signal to a power amplifier, in which: the rectangular-wave signal has a DC level defined by an adjustable threshold voltage level; a feedback loop includes: low-pass filter means provided for filtering the rectangular-wave signal; and comparison means provided for comparing a DC level of a filtered signal received from the low-pass filter means with a predefined reference level; the reference level is selected for cancelling out a given harmonic component; and the comparison means is configured to output a correction signal for adjusting the threshold voltage level of the first buffer means to the first buffer means.
That is, in the harmonic cancellation circuit for power amplifier disclosed in Japanese Unexamined Patent Application Publication No. 2015-115946, a harmonic distortion caused in a transmission signal is suppressed by detecting the DC level of the transmission rectangular-wave signal and comparing the detected DC level of the transmission rectangular-wave signal with the reference voltage so that a desired duty ratio is obtained.